Our research plan follows the long range goals stated in the initial proposal. Specifically we plan to - (a) Characterize by gel electrophoresis and peptide maps the Form I and II polyA polymerases and the co-factor responsible for chain elongation. (b) Purify and characterize the ribosomal associated ribonuclease which is responsible for degrading polyA. (c) Utilize our newly developed technique of RPC-5 columns for the fractionation of mRNA species. (d) Exploit the plasmids containing purified yeast DNA which have been cooperatively isolated at Brandeis this past year. Plasmids, containing selected yeast genomes, will be used as reagents to analyze mRNA populations produced at various intervals of the yeast cell cycle. BIBLIOGRAPHIC REFERENCES: Klar, A.J.S. and Halvorson, H.O. 1976. Effect of GAL4 Gene Dosage on the Level of Galactose Catabolic Enzymes in Saccharomyces cerevisiae. Journal of Bacteriology, Vol. 125, pp. 379-381. Klar, A.J.S., Cohen, A., and Halvorson, H.O. 1976. Control of Enzyme Synthesis and Stability During Sporulation in Saccharomyces cerevisiae. Biochimie, Vol. 58, pp. 219-224.